Organosilicon-mediated regioselective acetylation of carbohydrates

Abstract

Organosilicon-mediated, regioselective acetylation of vicinal- and 1,3-diols is presented. Methyl trimethoxysilane or dimethyl dimethoxysilane was first used to form cyclic 1,3,2-dioxasilolane or 1,3,2-dioxasilinane intermediates, and subsequent acetate-catalyzed monoacylation was efficiently performed by addition of acetic anhydride or acetyl chloride under mild conditions. The reaction exhibited high regioselectivity, resulting in the same protection pattern as in organotin-mediated schemes.

Regioselective Benzoylation of Diols and Carbohydrates by Catalytic Amounts of Organobase

“…The yield of 2 increased with the amount of DBU used up to 0.4 equiv (Entries 12, 13 and 14). [15][16][17][18]. The addition of DMF is not necessary for diols due to their good solubility in acetonitrile.…”

“…More specifically, developing environment-friendly, convenient, efficient and highly regioselective carbohydrate protection methods remains as one of the most prominent challenges [9]. Over the last several decades, many protection methods have been developed, including the use of reagents such as organotin [10][11][12], organoboron [13,14], organosilicon [15][16][17], metal salts [18][19][20][21][22][23], organobase [24][25][26], and enzymes [27][28][29][30]. Although these reagents each have advantages, they also possess troublesome shortcomings including inherent toxicity, high cost and the necessity to pre-protect secondary hydroxyl groups.…”

Regioselective Silyl/Acetate Exchange of Disaccharides Yields Advanced Glycosyl Donor and Acceptor Precursors

“…TLC (EA/Hex = 10:90) R f 0.53. [α] 25 D +80 (c 1.04, CHCl 3 ). 1 H NMR (800 MHz, CDCl 3 ) δ 4.95 (d, J = 3.1 Hz, 1H, H-1), 4.89 (d, J = 3.1 Hz, 1H, H-1′), 4.24 (dd, J = 11.9, 2.2 Hz, 1H, H-6a), 4.09 (dd, J = 11.9, 4.5 Hz, 1H, H-6b), 4.01 (ddd, J = 9.5, 4.4, 2.2 Hz, 1H, H-5), 3.91–3.88 (m, 2H, H-3, H-3′), 3.77 (dt, J = 9.4, 3.1 Hz, H5′), 3.66 (d, J = 3.1 Hz, 2H, H-6′ab), 3.48 (t, J = 9.1 Hz, 1H, H-4), 3.46 – 3.41 (m, 2H, H-4′, H-2), 3.39 (dd, J = 9.3, 3.1 Hz, 1H, H-2′), 2.10 (s, 3H), 0.14 (s, 9H), 0.138 (s, 9H), 0.137 (s, 9H), 0.13 (s, 9H), 0.12 (s, 18H), 0.08 (s, 9H).…”

“…TLC (EA/Hex = 1:9) R f 0.22. [α] 25 D +97 (c 0.77, CHCl 3 ). 1 H NMR (800 MHz, CDCl 3 ) δ 4.93 (d, J = 3.0 Hz, 2H, H-1, H-1′), 4.22 (dd, J = 11.9, 2.2 Hz, 2H, H-6a, H-6′a), 4.08 (dd, J = 11.9, 4.7 Hz, 2H, H-6b, H-6′b), 4.03 – 3.98 (m, 2H, H-5, H-5′), 3.90 (t, J = 9.0 Hz, 2H, H-3, H-3′), 3.50 – 3.44 (m, 4H, H-2, H-2′, H-4, H-4′), 2.09 (s, 6H), 0.14 (s, 18H), 0.14 (s, 18H), 0.12 (s, 18H).…”

“…23, 24 Chemical methods for the selective acylation of sugars have also had limited success. 10, 25 The main factor hindering progress in this area can be attributed to the insolubility of free sugars in organic solvents. Further complicating matters is anomalous behavior resulting from the hydrogen bonding network present in unprotected carbohydrates.…”